How much pressure? With a manual master cylinder and front discs, which do the majority of the braking, the pressure you apply is dependent on how quick you want to stop!!! Nailing them hard will stop the beast quickly and you've got time to sense what's going on without locking them up.
The problem I experienced with boosted brakes without ABS in pickups, was the tendency of your body weight shifting forward in the seatbelt and you applying more pressure than you needed even with the pedal ratio adjusted. They were okay during normal driving conditions but you had to watch hard braking situations. Once you lock things up momentarily, you will need to be quick to get things back under control. With the non-boosted brakes and an adjustable proportioning valve you can tune your rear brakes so you aren't fearful of locking everything up and loosing steering control. To me, being able to lock up your power boosted brakes with 10-12 lbs. of pedal pressure is like having a 1 lb. pull on the trigger of your favorite rifle. Not much room for error. On my brakes, I want a little more latitude before things start locking up.
Another thing to consider is the size of the booster and getting it plumbed in...especially if you're running an automatic transmission. Interference with the tranny crossmember can be an issue. Several of the Vendors are offering add-on inline pressure multipliers as well as a Hydraboost system that runs off the power steering pump along with the power steering gear box. CCP is selling their unit for less than a vacuum booster setup. I've not tried it yet but it appears to be a viable option.
Dave
